Digital cameras are being improved and lowered in cost at an amazing rate. In a recent year, more digital cameras were sold than traditional film cameras. Images from digital cameras can be downloaded and stored on personal computers. Digital pictures can be converted to common formats such as JPEG and sent as e-mail attachments or posted to virtual photo albums on the Internet. Video as well as still images can be captured, depending on the kind of digital camera.
FIG. 1 is a block diagram for a typical digital camera. Light focused through a lens is directed toward sensor 12, which can be a charge-coupled device (CCD) array or a complementary metal-oxide-semiconductor (CMOS) sensor array. The light falling on the array generates electrical currents, which are amplified by analog amp 14 before being converted from analog to digital values by A/D converter 16. An 8, 9, or 10-bit mono-color pixel is output to processor 10. These mono-color pixels are in a Bayer-pattern as shown in FIG. 2. Each pixel is either a red, a blue, or a green intensity.
The R, G, or B digital values in the Bayer pattern are processed by processor 10 to generate luminance-chrominance YUV pixels. The YUV pixels can then be displayed on display 19 or compressed by compressor 18 and stored on disk 17 or on a solid-state memory. YUV pixels often have a 4:4:4 format, with 8 bits for each of 2 colors and for the luminance.
Sensor 12 detects red, blue and green colors. However, each array point in sensor 12 can detect only one of the three primary colors. Rather than outputting an RGB pixel, sensor 12 can output only a single-color pixel at any given time. For example, a line of pixels output by sensor 12 might have a red pixel followed by a green pixel. Another line might have alternating green and blue pixels.
Each pixel represents the intensity of one of the primary colors at a point in the sensor array. Thus a red pixel indicates the intensity of red light at a point, while a neighboring green pixel indicates the intensity of green light at the next point in the sensor array. Each pixel contains only one-third of the total color information.
The remaining color information is obtained by interpolation. The green intensity of a red pixel is calculated by averaging the green intensities of neighboring green pixels. The blue intensity for that red pixel is calculated by averaging or interpolating the nearest blue pixels. Processor 10 performs this color interpolation, calculating the missing primary-color intensities for each pixel location.
Processor 10 also may perform other enhancements to the image. Edges may appear fuzzy because the color interpolation tends to spread out features. These edges can be sharpened by detecting the edges and enhancing the color change at the edge to make the color transition more abrupt. Color conversion from RGB to YUV is also performed by processor 10.
The electrical currents produced by the different primary colors can vary, depending on the sensor used and the wavelength and energy of the light photons. An adjustment known as a white-balance is often performed before processor 10, either on analog or digital values. Each primary color can be multiplied by a different gain to better balance the colors. Compensation can also be made for different lighting conditions, increasing all primary colors for dark pictures or decreasing all colors for bright pictures (overexposure).